title: Effects of Neurally Adjusted Ventilatory Assist (NAVA) levels in non-invasive ventilated patients: titrating NAVA levels with electric diaphragmatic activity and tidal volume matching.
abstract: BACKGROUND
  Neurally adjusted ventilatory assist (NAVA) delivers pressure in proportion to diaphragm electrical activity (Eadi). However, each patient responds differently to NAVA levels. This study aims to examine the matching between tidal volume (Vt) and patients' inspiratory demand (Eadi), and to investigate patient-specific response to various NAVA levels in non-invasively ventilated patients.
  
  
  METHODS
  12 patients were ventilated non-invasively with NAVA using three different NAVA levels. NAVA100 was set according to the manufacturer's recommendation to have similar peak airway pressure as during pressure support. NAVA level was then adjusted ±50% (NAVA50, NAVA150). Airway pressure, flow and Eadi were recorded for 15 minutes at each NAVA level. The matching of Vt and integral of Eadi (ʃEadi) were assessed at the different NAVA levels. A metric, Range90, was defined as the 5-95% range of Vt/ʃEadi ratio to assess matching for each NAVA level. Smaller Range90 values indicated better matching of supply to demand.
  
  
  RESULTS
  Patients ventilated at NAVA50 had the lowest Range90 with median 25.6 uVs/ml [Interquartile range (IQR): 15.4-70.4], suggesting that, globally, NAVA50 provided better matching between ʃEadi and Vt than NAVA100 and NAVA150. However, on a per-patient basis, 4 patients had the lowest Range90 values in NAVA100, 1 patient at NAVA150 and 7 patients at NAVA50. Robust coefficient of variation for ʃEadi and Vt were not different between NAVA levels.
  
  
  CONCLUSIONS
  The patient-specific matching between ʃEadi and Vt was variable, indicating that to obtain the best possible matching, NAVA level setting should be patient specific. The Range90 concept presented to evaluate Vt/ʃEadi is a physiologic metric that could help in individual titration of NAVA level.
authors.affiliation: Department of Mechanical Engineering, University of Canterbury, Christchurch, New Zealand.
authors.forename: Yeong Shiong
authors.initials: YS
authors.lastname: Chiew
authors.forename: J Geoffrey
authors.initials: JG
authors.lastname: Chase
authors.forename: Bernard
authors.initials: B
authors.lastname: Lambermont
authors.forename: Jean
authors.initials: J
authors.lastname: Roeseler
authors.forename: Christopher
authors.initials: C
authors.lastname: Pretty
authors.forename: Emilie
authors.initials: E
authors.lastname: Bialais
authors.forename: Thierry
authors.initials: T
authors.lastname: Sottiaux
authors.forename: Thomas
authors.initials: T
authors.lastname: Desaive
mesh_terms: D000368:Aged; D003964:Diaphragm / Q000503:physiopathology*; D055724:Electrophysiological Phenomena; D005260:Female; D006801:Humans; D001239:Inhalation / Q000502:physiology; D059725:Interactive Ventilatory Support / Q000379:methods*; D008297:Male; D008875:Middle Aged; D057285:Precision Medicine; D013990:Tidal Volume